<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>登录</title>
    <style>
        body{
            margin: 0;
            padding: 0;
            font-family: sans-serif;
            background-image: url(img/bg1.jpg);
            background-repeat: no-repeat;
            background-size: cover;
        }
        .box{
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%,-50%);
            width: 400px;
            padding: 40px;
            background: rgba(24, 23, 23, 0.8);
            box-sizing: border-box;
            box-shadow: 0 15px 25px rgba(0,0,0,.5);
            border-radius: 10px;
        }
        .box h2{
            margin: 0 0 40px;
            padding: 0;
            color: #fff;
            text-align: center;
        }
        .box .inputBox{
            position: relative;
        }
        .box .inputBox input{
            width: 90%;
            padding: 10px 0;
            font-size: 16px;
            color: #fff;
            letter-spacing: 1px;
            margin-bottom: 20px;
            border: none;
            border-bottom: 1px solid #fff;
            outline: none;
            background: transparent;
        }
        .box .inputBox label{
            position: absolute;
            top: 0;
            left: 0;
            padding: 10px 0;
            font-size: 16px;
            color: #fff;
            pointer-events: none;
            transition: .5s;
        }
        .box .inputBox input:focus ~ label,
        .box .inputBox input:valid ~ label
        {
            top:-18px;
            left: 0;
            color: #03a9f4;
            font-size: 12px;
        }
        .box input[type="submit"]{
            background: transparent;
            border: none;
            outline: none;
            color: #fff;
            background: rgba(236, 196, 125, 0.76);
            padding: 10px 20px;
            border-radius: 10px;
            cursor: pointer;
            margin: 0 100px 0 100px;
        }
    </style>
</head>
<body>
    <div class="box">
        <h2>Login</h2>
        <form>
            <div class="inputBox">
                <input type="text" name="" required="" />
                <label>Username</label>
            </div>
            <div class="inputBox">
                <input type="password" name="" required="" />
                <label>password</label>
            </div>
            <input type="submit" name="" value="submit" />
        </form>
    </div>
</body>
</html>